1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device having a trench.
2. Description of the Related Art
Semiconductor devices have been advancing while reducing in size with the progress of time. A general method for size reduction is a pattern reduction in a plane by making full use of a miniaturization technology. The method is, however, approaching its limit in recent years, and hence size reduction of semiconductor devices using a three-dimensional structure, in which a depth direction of a semiconductor substrate is effectively used, has been newly attempted. Under those circumstances, a trench etching technique becomes indispensable. However, in the existing trench etching technique, a variation in trench depth direction is not small, which is a major problem in semiconductor devices in which characteristics are largely changed due to a size change in a depth direction. A technique frequently used to improve the variation is a manufacturing method using a stopper film. Conceptual views of the invention are illustrated in FIG. 3.
An etching stopper film 4, a to-be-trench-etched film 5, and a resist 6 are deposited on a semiconductor substrate 1 in this order, and the resist 6 is patterned (FIG. 3A). Here, a substance having a high etching selectivity with respect to the to-be-trench-etched film 5 is used for the etching stopper film 4. Next, the resist 6 is used as a mask to etch the to-be-trench-etched film 5. Since the etching is stopped at the etching stopper film 4, the depths of trenches formed in the to-be-trench-etched film 5 become constant. (For example, see JP 2001-185532 A)
In the method of the above-mentioned conventional art, however, formation of the etching stopper film 4 made of a substance different from the to-be-trench-etched film 5 is required immediately below the to-be-trench-etched film 5, which makes manufacturing steps complicated and causes an increase in cost. In addition, the to-be-trench-etched film 5 is deposited on the etching stopper film 4, causing inconvenience such as a physical limitation or defective electrical connection with the semiconductor substrate 1. In particular, this method cannot be used to form a trench directly on the silicon substrate 1.